Vibration resistant coupling

ABSTRACT

A vibration resistant coupling for use in coupling tubular ducts and the like. The coupling includes a seal structure including a ring formed of an elastomeric material. Within the elastomeric ring is a substantially rigid gripping element and means responsive to an axial compression of the ring to urge the gripping element into gripping association with the outer wall of a tubular duct extended therethrough. The means for constricting the gripping element may comprise wedge means disposed within the elastomeric ring and may include at least one wedge surface on the gripping element. The wedge means is arranged to effectively retain the gripping element in association with the tubular duct notwithstanding a lessening of the compressive force exerted on the gripping element by the elastomeric ring.

United States Patent Kotsakis [$4] VIBRATION RESISTANT COUPLING [72]inventor: Mike D. Kotsaltis, Des Plaines, ill.

[73] Assignee: Imperial-Eastman Corporation [22] Filed: Sept. 11, 1970[21] Appl. No.: 71,543

[52] US. Cl. ..285/343, 285/348, 285/382.7 [51] Int. Cl ..F16l 19/08[58] Field 01 Search ..285/34l, 348, 343, 421, 342,

[56] References Cited UNITED STATES PATENTS 3,485,517 12/1969 Howe..285/348 X 3,207,523 9/1965 Johnson ..277/l90 X 3,441,297 4/1969 Koski..285/348 X 2,448,888 9/1948 l-lynes ..285/340 X 3,434,744 3/1969 Yokeet a1. ..285/348 X 2,394,351 2/1946 Wurzburger ..285/341 2,613,08610/1952 Wolfram ..285/348 X 2,391,900 1/1946 Hobbs ..285/341 2,931,6714/1960 Beeley ..285/341 X FOREIGN PATENTS OR APPLICATlONS 503,088 7/1930Germany ..277/35 1 Aug. 15, 1972 831,127 3/1960 GreatBritain.............285/34l 551,006 2/1943 Great Britain ..285/34321,718 1 1/1893 Great Britain ..277ll45 1,146,673 3/1969 Great Britain..285/341 Primary Examiner-Thomas F. Callaghan Attorney-Hofgren, Wegner,Allen, Stellman & Mc- Cord ABSTRACT A vibration resistant coupling foruse in coupling tubular ducts and the like. The coupling includes a sealstructure including a ring formed of an elastomeric material. Within theelastomeric ring is a substantially rigid gripping element and meansresponsive to an axial compression of the ring to urge the grippingelement into gripping association with the outer wall of a tubular ductextended therethrough. The means for constricting the gripping elementmay comprise wedge means disposed within the elastomeric ring and mayinclude at least one wedge surface on the gripping element. The wedgemeans is arranged to effectively retain the gripping element inassociation with the tubular duct notwithstanding a lessening of thecompressive force exerted on the gripping element by the elastomericring.

21 Claims, 8 Drawing Figures PITE'NTEMMS m2 3.684.322

saw a nr 2 VIBRATION RESISTANT COUPLING BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to couplings and inparticular to couplings for use with tubular ducts.

2. Description of the Prior Art In couplings for coupling tubular ducts,means are conventionally provided for securing the duct end againstaxial withdrawal from the coupling. Such means comprise constrictiblesleeve elements which are urged into gripping engagement with the ductend as a result of making up of the fitting.

In certain installations, substantial vibration may be present tendingto relax the gripping of the duct end with subsequent undesirablerelease thereof from the coupling.

Another problem encountered at times in the coupling of tubular ducts isthe desirability to accommodate some skewing of the axis of the ductrelative to the axis of the coupling. To this end, nonrigid, orresilient, gripping elements have been employed.

In such couplings, it is further conventional to provide resilientsealing means caused to effect a seal between the duct end and thecoupling elements as a result of making up of the fitting. Many forms ofsuch sealing elements are utilized in the coupling art.

SUMMARY OF THE INVENTION The present invention comprehends an improvedcoupling for use with a tubular duct effecting an improved positiveretention of the duct end in association with the coupling and apositive sealed connection of the duct end thereto.

More specifically, the invention comprehends providing a coupling havinga novel seal structure including a ring formed of elastomeric materialand having a radially inwardly opening groove, an annular retainer ringdefining a gripping element coaxially within the groove, and meanswithin the groove responsive to a shortening of the axial extent of thering to urge the gripping element radially inwardly.

The means for urging the gripping element inwardly may comprise wedgingmeans which may include at least one frustoconical surface on theannular gripping element engaged by a cooperating wedging elementdisposed within the elastomeric ring. The wedging element may comprisean annular member having a corresponding frustoconical wedging surfaceabutting the wedging surface of the gripping element. The angle of thefrustoconical surfaces is preferably preselected to be no greater thanthe friction locking angle whereby the wedging element effectivelypositively retains the gripping element in locked association with theduct end. Thus, the gripping element is retained in the fullyconstricted, or innermost, disposition by the frictional retentionthereof notwithstanding a release in the forces produced thereon by theelastomeric ring. Thus, for example, where the ring is formed of rubber,a cold flow, or set, of the rubber after a period of time will notresult in a release of the gripping element notwithstanding the releaseof the constricting forces. Thus, cyclic stress of the duct end iseffectively precluded, substantially increasing the life of the couplingand more specifically, increasing the resistance of the duct end tofailure at the retainer ring as often occurs in conventional couplingswherein cyclic changes in the gripping action of retaining elements mayoccur.

Alternatively, the wedging element may comprise an annular elementhaving a circular cross-section in an axial plane.

The gripping element may include a pair of frustoconical surfacesnarrowing oppositely outwardly from each other and the end arranged tobe engaged by a pair of complementary wedging elements urged forciblyagainst the wedging surface of the gripping element as a result of thecompression of the elastomeric ring. The elastomeric ring may comprise apair of ring elements cooperatively defining the inwardly openinggroove. Alternatively, the ring may comprise a unitary ring. In oneform, the ring may have a slit extending partially radially outwardlyfrom the groove.

The gripping element may be provided with a cylindrical radially innersurface. Alternatively, the gripping element may be provided with one ormore radially inwardly projecting annular teeth for biting into the ductend in the make-up of the coupling. The gripping element may comprise asplit retainer ring.

The resilient ring and the wedging means may be provided with abuttingplanar surfaces for transmission of axial forces from the resilient ringto the wedging means as a result of the axial compression of theresilient ring during make-up of the coupling. The coupling elements arefurther constricted to permit a flow of the resilient ring materialsuitably to accommodate any excessive compressive force exerted thereonso as to further provide an effective limitation on the amount of forceapplied by the resilient means to the wedging means while yet permittingthe outer means to effectively bottom out, or provide a desirablehit-home indication.

The coupling includes outer means for effecting a compression of theelastomeric ring which may include positive limit stop means forlimiting the amount of compression applicable to the elastomeric ring inthe make-up of the coupling. In the illustrated embodiment, the outermeans comprises nut and body members having cooperating shoulderslimiting the advance of the nut on the body member to a preselectedposition whereby the desired control of the compression of theelastomeric means is obtained.

The invention further comprehends providing means associated with thewedge means for limiting the amount of constriction of the retainerring, or gripping element. More specifically, the wedging means maycomprise a pair of gripping elements having opposing surfaces whichsubstantially abut in a limiting position wherein the wedging action ofthe wedging means effects a preselected maximum constriction of thegripping element. In the preferred embodiment, the maximum constrictionof the gripping element permits the duct end to remain substantiallyunconstricted.

BRIEF DESCRIPTION OF THE DRAWING Other features and advantages of theinvention will be apparent from the following description taken inconnection with the accompanying drawing wherein:

FIG. I is a fragmentary front elevation of a coupling embodying theinvention having a tubular duct end associated therewith;

FIG. 2 is a fragmentary enlarged diametric section of the structure ofFIG. 1 with the coupling as arranged at the beginning of making upthereof;

FIG. 3 is a fragmentary enlarged diametric section similar to that ofFIG. 2 but with the coupling elements as arranged upon completion ofmake-up thereof;

FIG. 4 is a fragmentary diametric section illustrating a modified formof coupling embodying the invention wherein the gripping element isprovided with a substantially cylindrical radially inner surface;

FIG. 5 is a fragmentary enlarged diametric section of a further modifiedform of coupling embodying the invention wherein the resilient ringcomprises a pair of annular elements;

FIG. 6 is a fragmentary enlarged diametric section of a still furthermodified form of coupling embodying the invention wherein the wedgemeans defines a single pair of frustoconical surfaces and a pair ofabutting planar surfaces;

FIG. 7 is a fragmentary enlarged diametric section of a yet furthermodified form of coupling embodying the invention wherein the wedgemeans comprises elements having circular cross section in an axialplane; and

FIG. 8 is a fragmentary diametric section illustrating a furthermodified form of coupling embodying the invention wherein the resilientring is provided with a slit extending radially outwardly therethrough.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the exemplary embodiment ofthe invention as disclosed in FIGS. l3 of the drawing, a couplinggenerally designated 10 for use in coupling the end 11 of a tubular ductis shown to comprise a body member 12 and a nut member 13 defining anouter encircling structure of the coupling. Body 12 and nut 13 areprovided with cooperating thread means 14 and 15 respectively, foradjustably spacing an intumed end flange 16 of the nut from an inner endcam portion 17 of the body as an incident of threading of the nut ontothe body thread 14.

Duct end 11 is sealingly retained in association with coupling 10 bymeans of a seal structure generally designated 18. As shown in FIG. 2,seal structure 18includes a sealing and force transmitting ring 19formed of elastomeric material and having a radially inwardly openinggroove 20. Received within groove 20 is a gripping element, or retainerring, 21 and wedging means generally designated 22. In the specificembodiment of coupling 10, the wedging means includes a pair of wedgerings 23 at axially opposite sides of the retainer ring 21. wedgingmeans 22 further includes a wedging surface 24 provided on the retainerring 21 for cooperation with a wedging element 23 and in the illustratedembodiment, a pair of frustoconical surfaces 24 are provided on theretainer ring narrowing axially away from each other.

As shown in FIGS. 2 and 3, the bight portion 25 of ring 19 may comprisea tubular portion having an unconstricted outer diameter slightly lessthan the inner diameter of nut portion 15 and an inner diameter slightlygreater than the outer diameter of wedge rings 23. As shown in FIG. 8,the bight portion 525 of the U- shaped resilient ring 519 may beprovided with a slit 526 extending partially radially outwardlytherethrough to facilitate installation of the wedging elements andgripping element therein as well as facilitate axial compression andmovement of the wedging elements 23 axially towards each other to afinal juxtaposed disposition in the made-up arrangement of the coupling.

Each of the wedge elements 23 may be provided with a planar end surface27 and a frustoconical radially inwardly facing wedging surface 28complementary to the frustoconical wedging surfaces 24 of the retainerring. wedging elements 23 may comprise rigid rings fon'ned of a materialsuch as metal and retainer ring 21 may comprise a split metal ringadapted to be constricted by wedging elements 23 in climbing ontosurfaces 24 during make-up of the coupling. As shown in FIG. 3, theretainer ring may be provided with at least one annular radiallyinwardly projecting tooth 29 biting into the outer surface of the wallof duct end 11 in the made-up arrangement of the coupling. In themade-up arrangement, the wedge elements 23 may be substantially inabutment with each other to provide a hithome indication as a result ina sudden increase in the resistance of the coupling to torquing.

Coupling 10 further defines a plurality of different control structuresproviding improved facilitated proper make-up of the fitting withminimum effort while yet assuring long, positive coupling of the ductend notwithstanding forces acting thereon tending to break theconnection. More specifically, as best seen in FIGS. 2 and 3, nut member13 may be provided with an inner end surface 34 confronting an outer endsurface 35 on body member 12 which are brought into abutment in themade-up arrangement of the fitting as seen in FIG. 3 to provide apositive hit-home indication of the completion of the assembly. In thefully made-up disposition of the coupling, sufficient force has beentransmitted through resilient ring 19 to urge wedging elements 23axially together to a final disposition as shown in FIG. 3 wherein thewedging elements effectively abut each other to limit the radialconstriction of the retainer ring gripping element 21. The constrictionthusly obtained is preselected to assure that the teeth 29 penetrate thewall of duct end 11 to the full radial extent of the teeth to provideeffectively maximized mechanical retention of the ring 21 againstwithdrawal of the duct end 11 axially therefrom. The constriction ofring 21 is further preselected to effectively preclude collapse of ductend 1 1 thereat to further maximize the strength of the couplingconnection.

As seen in FIG. 3, the elastomeric ring material tends to flow throughthe tubular spaces 36 and 37 between duct end 11 and nut flange 16 atthe outer end of the coupling and between duct end 11 and body member 12at the inner end of the coupling, thereby to provide control over themaximum compressive force generated by the resilient ring on the wedgingelements. Thus, manufacturing tolerances on the nut and body dimensionsare not extreme as the permissible rubber deformation into spaces 36 and37 provides a control over the transmission of forces to the grippingelement from the threaded advancement of the nut on the body. Ring 19provides a seal between the duct end 11 and the body member 12. Asecondary seal may be effected between the nut member and the duct endsimilarly by ring 19 for further improved performance of the sealstructure defined by the elastomeric ring retainer element and wedgingmeans.

Retainer ring 21 is effectively positively retained in its innermostconstricted disposition by a locking action developed between the wedgerings 23 and the retainer ring 21 to effectively avoid cyclic stressesin the duct end. More specifically, the invention comprehends providingsurfaces 24 and 28 at an angle preselected to be no greater than thefriction locking angle whereby wedging elements 23 are frictionallylocked in the constricting disposition of FIG. 3 upon completion of themake-up of the coupling. Thus, should the resilient ring 19 cold flow,or otherwise relax the compressive force thereof acting on wedgingelements 23, the wedging elements do not move outwardly to relax theirconstricting effect on the gripping element, but rather, positivelymaintain the gripping element in the duct end gripping disposition ofFIG. 3. Illustratively, where the elements 21 and 23 are formed ofsteel, the angle of surfaces 24 and 28 may be approximately 24 to theaxis of the coupling. As will be obvious to those skilled in the art,the friction locking angle, i.e., an angle whose tangent is equal to thecoefficient of friction of the confronting surfaces, may vary as afunction of a number of parameters such as the material of which theelements are formed, the surface conditions thereof such as oxidation,contamination, presence of lubricant, etc.

Thus, in making up of coupling 10, the user firstly installs the wedgingelements 23 and retainer ring 21 in groove of the resilient ring 19, asshown in FIG. 2. The preassembled seal structure 18 is then installedwithin the nut 13 whereupon the nut may be threaded onto the body memberthread 14 as shown in FIG. 2 to compress the seal structure 18 betweenflange 16 and body cam portion 17. As the resilient ring 19 iscompressed, it transfers axial force to each of the wedge elements 23through the planar outer surfaces 27 to move the wedge elements 23axially onto frustoconical surfaces 24 of retainer ring 21 therebyconstricting the retainer ring. The constriction of retainer ring 21 iscontinued until surfaces 34 and 3S abut, at which point, wedgingelements 23 are brought into substantial abutment and teeth 29 aresubstantially fiilly embedded in the wall of duct end 11. At this time,resilient ring 19 has been deformed to substantially completely fill thespace within nut 13 and sealingly engage the outer surface of the ductend about retainer ring 21 and wedging means 22, as shown in FIG. 3. Asretainer ring 21 is positively retained on the duct end and resilientlyassociated with the coupling elements 12 and 13 through the medium ofthe resilient ring 19 therebetween, a positive high flexure, vibrationresistant coupling is provided wherein the duct end is effectivelymaintained sealed to body member 12 and retained against pullout, oraxially outward displacement, from the coupling notwithstanding suchvibration and other forces tending to urge the duct end outwardlytherefrom. Further, as the retainer ring is effectively carried withinthe resilient ring 19, the duct end 11 may have a skewed relationship tobody 12 while yet a positive sealed connection therebetween may beeffected by means of seal structure l8.

lllustratively, a nominal 1% inches coupling made in conformity with thecoupling corresponding to the disclosed coupling 10 has been found tohave a burst strength of approximately 13,000 psi. Because of thevibration resistant characteristics of seal structure 18, a much lowerratio of the normal rating to the burst strength may be utilized. Thus,illustratively, a nominal rating of approximately 3,250 psi may beutilized with the indicated 1% inches coupling whereas in conventionalcouplings, a rating of under 1,500 psi would be conventionally applied.

A further feature of the seal structure 18 is the adaptability for usethereof with conventional couplings utilizing nut and body membersgenerally similar to nut and body members 13 and 12 of coupling 10.

In the illustrated embodiment, teeth 29 may be disposed as desired atany portion axially of the retainer ring and may comprise asymmetricalteeth wherein the outer surface may be at an angle of approx. to theaxis of the coupling and the inner surface may be at an angle of approx.45 thereto.

Referring now to the embodiment of FIG. 4, a modified form of couplinggenerally designated is shown to comprise a coupling generally similarto coupling 10 but having a modified form of retainer ring generallydesignated 121 provided with a cylindrical radially inner surface freeof radial inward projections such as teeth 29 whereby the retainer ringretains the duct end 1 l with a frictional grip.

In FIG. 5, a further modified form of coupling generally designated 210is shown to comprise a coupling generally similar to coupling 10 butwherein the annular resilient ring 219 comprises a split ringeffectively defined by a pair of resilient ring elements 219a and 2l9bcooperatively defining the radially inwardly opening groove 220.

In FIG. 6, a still further modified form of coupling embodying theinvention generally designated 310 is shown to comprise a couplinggenerally similar to coupling 10 but having a seal structure generallydesignated 318 wherein the retainer ring 321 is provided with a singlefrustoconical surface 324. A single wedge element 323 is provided forwedging coaction with a wedge surface 324 and a rigid back-up ring 331is provided with a planar surface 332 abutting a planar end surface 333of the modified retainer ring 321.

As shown in FIG. 7, a still further modified coupling 410 is similar tocoupling 10 except that the wedging elements 423 comprise metal ringshaving circular cross-sections in an axial plane, i.e. a plane of theaxis of the coupling and of the annular extent of rings 423.

The modification of FIG. 8 as discussed above comprises a coupling 510similar to coupling 10 except having slit 526 provided therein tofacilitate make-up of the coupling.

Each of the couplings 110, 210, 310, 410 and 510 is similar to andfunctions similar to coupling 10 except as otherwise .noted above.Elements of couplings 110, 210, 310, 410 and 510 similar tocorresponding elements of coupling 10 are identified by similarreference numbers, but respectively 100 higher. The variousmodifications of couplings 110, 210, 310, 410 and 5 10 are exemplary ofmodifications of the broad structural concepts which may be embodied inthe invention.

The foregoing disclosure of specific embodiments is illustrative of thebroad inventive concepts comprehended by the invention.

lclaim:

l. A coupling for use with a tubular duct, comprising: a contractibleretainer ring having an original inner diameter at least substantiallyequal to the outer diameter of the duct to be coupled and an outersurface; rigid ring-like wedge means wedgedly engaging said outersurface of said retainer ring and having axially opposite end portionsand a radially outer external surface, said wedge means comprising meansfor contracting said retainer ring grippingly about the duct as theresult of application of opposing forces acting against said oppositeend portions; and outer means for adjustably enclosing said associatedretainer ring and wedge means and having resilient means surroundingsaid opposite end portions and the entire said external surface of saidwedge means and extending into engagement with the duct in the made-uparrangement of the coupling, said resilient means being arranged toresiliently apply opposing forces to said wedge means end portions forcontracting said retainer ring as a result of adjustment of said outermeans.

2. The coupling of claim 1 wherein said resilient means comprises a ringcoaxially of said retainer ring and defining a radially inwardly openingannular groove receiving said associated retainer ring and wedge means.

3. The coupling of claim 1 wherein said retainer outer surface comprisesan outwardly inclined frustoconical surface and said wedge meanscomprises a wedge ring having a complementary inwardly inclinedfrustoconical surface facially engaging said retainer ring inclinedsurface.

4. The coupling of claim I wherein said wedge means comprises a pair ofrigid rings one each at opposite axial ends of said retainer ring, saidretainer ring outer surface comprising an outwardly inclinedfrustoconical surface, one rigid ring bearing against said outwardlyinclined surface.

5. The coupling of claim I wherein said wedge means comprises a pair ofrigid rings one each at opposite axial ends of said retainer ring, saidretainer ring outer surface being defined by a pair of axiallyoppositely, outwardly inclined frustoconical surfaces, one of said rigidrings engaging one of said inclined retainer ring inclined surfaces andthe other of said rigid elements engaging the other of said inclinedretainer ring inclined surfaces.

6. The coupling of claim 1 wherein said retainer ring outer surfacecomprises a frustoconical surface and said wedge means comprises anannular element coaxially engaging said frustoconical surface.

7. The coupling of claim 6 wherein said annular element has a circularcross section in a plane of the axis of annularity thereof.

8. The coupling of claim 6 wherein said annular element has afrustoconical surface facially engaging said retainer ring frustoconicalsurface.

9. The coupling of claim 1 wherein said retainer ring includes a planarend surface and said wedge means includes a back-up element having anend surface engag- 'iif'ifiis fii in g t if claim 9 wherein said back-upelement end surface is planar and facially engages said retainer ringplanar surface.

1 l. The coupling of claim 1 wherein said resilient means comprises apair of coaxial annular elements cooperatively defining a radiallyinwardly opening groove, said associated retainer ring and wedge meansbeing disposed in said groove.

12. The coupling of claim 1 wherein said resilient means comprises anannular member having a radially inwardly opening U-shaped cross-sectionin an axial plane.

13. The coupling of claim 12 wherein said annular member defines a bightportion having a split extending radially partially through the radialthickness thereof.

14. The coupling of claim 1 wherein said retainer ring is provided witha substantially annular tooth projecting radially inwardly therefrom tobite into the tubular duct in the made-up arrangement of the coupling.

15. The coupling of claim 1 wherein said wedge means and resilient meanshave planar surfaces abutting each other for transferring an axial forcefrom the resilient means to the wedge means suitable to urge said wedgemeans against the retainer ring to contract the retainer ring intopositive gripping engagement with the tubular duct.

16. The coupling of claim 1 wherein said retainer ring outer surfacecomprises an outwardly inclined surface and said wedge means comprisesan element having a complementary inwardly inclined surface faciallyengaging said retainer ring inclined surface, said surfaces being at anangle preselected to be no greater than the friction locking anglewhereby said wedge element locks said retainer ring in an innermostcontracted disposition.

17. The coupling of claim 1 wherein said outer means is provided withmeans for positively limiting the amount of force applied by saidresilient means to said wedge means.

18. The coupling of claim 1 wherein said wedge means comprises a pair ofapposed ring-like wedge elements provided with means for limiting thecontraction of said retainer ring effected by said wedge means.

19. The coupling of claim 16 wherein said wedge means and said retainerring are formed of steel and said wedge inclined surfaces are at anangle to the axis thereof of no greater than approximately 24 wherebysaid wedging element locks said retainer element in a radially inwardlyconstricted disposition.

20. The seal structure of claim 1 wherein said wedge means comprises aplurality of rigid rings.

21. The seal structure of claim 1 wherein said retainer ring is formedof metal.

1. A coupling for use with a tubular duct, comprising: a contractibleretainer ring having an original inner diameter at least substantiallyequal to the outer diameter of the duct to be coupled and an outersurface; rigid ring-like wedge means wedgedly engaging said outersurface of said retainer ring and having axially opposite end portionsand a radially outer external surface, said wedge means comprising meansfor contracting said retainer ring grippingly about the duct as theresult of application of opposing forces acting against said oppositeend portions; and outer means for adjustably enclosing said associatedretainer ring and wedge means and having resilient means surroundingsaid opposite end portions and the entire said external surface of saidwedge means and extending into engagement with the duct in the made-uparrangement of the coupling, said resilient means being arranged toresiliently apply opposing forces to said wedge means end portions forcontracting said retainer ring as a result of adjustment of said outermeans.
 2. The coupling of claim 1 wherein said resilient means comprisesa ring coaxially of said retainer ring and defining a radially inwardlyopening annular groove receiving said associated retainer ring and wedgemeans.
 3. The coupling of claim 1 wherein said retainer outer surfacecomprises an outwardly inclined frustoconical surface and said wedgemeans comprises a wedge ring having a complementary inwardly inclinedfrustoconical surface facially engaging said retainer ring inclinedsurface.
 4. The coupling of claim 1 wherein said wedge means comprises apair of rigid rings one each at opposite axial ends of said retainerring, said retainer ring outer surface comprising an outwardly inclinedfrustoconical surface, one rigid ring bearing against said outwardlyinclined surface.
 5. The coupling of claim 1 wherein said wedge meanscomprises a pair of rigid rings one each at opposite axial ends of saidretainer ring, said retainer ring outer surface being defined by a pairof axially oppositely, outwardly inclined frustoconical surfaces, one ofsaid rigid rings engaging one of said inclined retainer ring inclinedsurfaces and the other of said rigid elements engaging the other of saidinclined retainer ring inclined surfaces.
 6. The coupling of claim 1wherein said retainer ring outer surface comprises a frustoconicalsurface and said wedge means comprises an annular element coaxiallyengaging said frustoconical surface.
 7. The coupling of claim 6 wherEinsaid annular element has a circular cross section in a plane of the axisof annularity thereof.
 8. The coupling of claim 6 wherein said annularelement has a frustoconical surface facially engaging said retainer ringfrustoconical surface.
 9. The coupling of claim 1 wherein said retainerring includes a planar end surface and said wedge means includes aback-up element having an end surface engaging said planar surface. 10.The coupling of claim 9 wherein said back-up element end surface isplanar and facially engages said retainer ring planar surface.
 11. Thecoupling of claim 1 wherein said resilient means comprises a pair ofcoaxial annular elements cooperatively defining a radially inwardlyopening groove, said associated retainer ring and wedge means beingdisposed in said groove.
 12. The coupling of claim 1 wherein saidresilient means comprises an annular member having a radially inwardlyopening U-shaped cross-section in an axial plane.
 13. The coupling ofclaim 12 wherein said annular member defines a bight portion having asplit extending radially partially through the radial thickness thereof.14. The coupling of claim 1 wherein said retainer ring is provided witha substantially annular tooth projecting radially inwardly therefrom tobite into the tubular duct in the made-up arrangement of the coupling.15. The coupling of claim 1 wherein said wedge means and resilient meanshave planar surfaces abutting each other for transferring an axial forcefrom the resilient means to the wedge means suitable to urge said wedgemeans against the retainer ring to contract the retainer ring intopositive gripping engagement with the tubular duct.
 16. The coupling ofclaim 1 wherein said retainer ring outer surface comprises an outwardlyinclined surface and said wedge means comprises an element having acomplementary inwardly inclined surface facially engaging said retainerring inclined surface, said surfaces being at an angle preselected to beno greater than the friction locking angle whereby said wedge elementlocks said retainer ring in an innermost contracted disposition.
 17. Thecoupling of claim 1 wherein said outer means is provided with means forpositively limiting the amount of force applied by said resilient meansto said wedge means.
 18. The coupling of claim 1 wherein said wedgemeans comprises a pair of apposed ring-like wedge elements provided withmeans for limiting the contraction of said retainer ring effected bysaid wedge means.
 19. The coupling of claim 16 wherein said wedge meansand said retainer ring are formed of steel and said wedge inclinedsurfaces are at an angle to the axis thereof of no greater thanapproximately 24* whereby said wedging element locks said retainerelement in a radially inwardly constricted disposition.
 20. The sealstructure of claim 1 wherein said wedge means comprises a plurality ofrigid rings.
 21. The seal structure of claim 1 wherein said retainerring is formed of metal.